Clamp for adjustable height scaffolds

ABSTRACT

A lock for mounting an angle bracket on a dimpled upright comprising a first side member and a second side member, a load bearing inner jaw and a load bearing outer jaw coupled to the side members with at least one of the jaws comprising a roller jaw having a size and shape to matingly engage with at least one dimple on a dimpled upright surface without marking or galling the upright surface, and a mounting device adapted to couple the side members to the angle bracket with the side members rotatable about a pivot axis of the mounting device relative to the angle bracket.

CROSS REFERENCE TO RELATED APPLICATIONS

None

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None

REFERENCE TO A MICROFICHE APPENDIX

None

FIELD OF THE INVENTION

This invention relates generally to adjustable height platform supports and more specifically, to an improved clamp for adjustable height scaffolds.

BACKGROUND OF THE INVENTION

Adjustable height platform supports are well known in the art and are generally used to perform elevated work in the construction and renovations of buildings. The adjustable height platform supports typically comprise four main elements, namely an upright, a bracket assembly for supporting a platform, a jack or “block and tackle” for raising and lowering the bracket assembly on the upright, and a means for holding the upper end of the upright in place.

Two types of adjustable height platform supports with uprights constructed of wood or rubber-backed aluminum are well known and widely used in the art. An example of an adjustable height platform support with the upright constructed of wood is shown in Hoitsma U.S. Pat. No. 2,216,912. The Hoitsma patent discloses a bracket assembly in which a jack is used to raise and lower the bracket assembly. This type of bracket assembly is referred to as a pump jack, which typically includes a frame having an upper and a lower shackle member supported by the frame.

Another example of an adjustable height platform support with a wooden upright is shown in U.S. Pat. No. 2,342,427 to Henry J. Riblet (herein after “Riblet '427 patent”). The Riblet '427 patent discloses a bracket assembly that is raised and lowered by a “block and tackle.” This type of bracket assembly that is mounted on an upright has been commonly referred to in the art as the “Painter's Pole.” In the Painter's Pole bracket assembly, an inner jaw of a shackle of the Painter's Pole bracket assembly is located below a plane containing both the fulcrum axis and an outer jaw of the shackle. A load on the angle bracket of the Painter's Pole bracket assembly provides a turning movement on the shackle, which activates the shackle by bringing both jaws, namely the outer jaw and an inner jaw of the shackle into contact with the upright when the width of the upright exceeds a “design width,” thereby activating the lock. Accordingly, a load actuated lock which function in this manner is referred to as a load activated lock.

Examples of adjustable height platform supports, which use an aluminum upright to include U.S. Pat. No. 4,597,471 to Anderson and U.S. Pat. No. 5,259,478 to Berish et al. It should be noted that the Anderson patent and the Berish patent both adapt aspects of the Hoitsma pump jack mechanism.

Although the adjustable height platform supports of the prior art generally works for their intended purpose, one of the major problems associated with the use of adjustable height scaffolds is the propensity of the shackles to lose its grip on the upright, especially after the uprights have been worn down through prolonged or extensive use, thereby resulting in the uncontrolled sliding of the adjustable height platform supports down the upright which can lead to worksite accidents.

In attempts to solve the above, U.S. Pat. No. 4,382,488 to Anderson teaches an adjustable platform supports that includes the use of an aluminum upright having a rubber strip containing rivets attached to a surface of the aluminum upright in order to help the shackles grip on the upright. However, backing an aluminum upright with a strip of rubber introduces notable drawbacks including but not limited to significantly increasing both the weight and the cost of the upright while making the safety of the scaffold dependent on the reliability of the rubber strip and the rivets and the adhesive that attaches the rubber strip to the upright.

BRIEF SUMMARY OF THE INVENTION

The present invention generally comprises an improved clamping system for adjustable height scaffolds that includes an upright having a dimpled upright surface with at least one dimple located thereon and a load bearing jaw of a shackle or lock having a size and shape for matingly engaging the at least one dimple of the upright to prevent uncontrolled sliding of the adjustable height platform supports down the upright without damaging the dimpled upright surface.

In one embodiment of the present invention, the shackle or lock comprises a pair of side members having an inner roller jaw and an outer roller jaw coupled to the side members with at least one of the jaws comprising a load bearing jaw having a plurality of rollers each pivotally mounted on a pair of side plates. The plurality of rollers are each sized and shaped to engage the dimpled upright surface to help prevent uncontrolled sliding of the adjustable height platform supports down the upright without marking, galling, or damaging the dimpled upright surface thereby prolonging the life of the upright. The lock also includes a fulcrum bar adapted to couple the side members to an angle bracket with the side members rotatable about an axis of the fulcrum bar relative to the angle bracket.

DESCRIPTION OF THE PRIOR ART

U.S. Pat. No. 2,216,912 teaches a bracket assembly in which a jack is used to raise and lower the bracket assembly.

U.S. Pat. No. 2,342,427 teaches a bracket assembly, which is raised and lowered by the “block and tackle.”

U.S. Pat. No. 4,382,488 teaches a pump jack upright pole formed of an elongated metal pole having a rubberized surface formed on only one aide of the metal pole.

U.S. Pat. No. 4,597,471 teaches a pump jack release mechanism actuated without the operator having to extend the operator's foot over an edge of the platform.

U.S. Pat. No. 5,259,478 teaches a pump jack having a protective cover for a crank down portion of the pump jack to avoid hazards upon wear of the roller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a bracket assembly mounted on a dimpled upright;

FIG. 1A shows a close-up side view of the load-activated lock of FIG. 1;

FIG. 2 shows an alternative embodiment of a bracket assembly mounted on a dimpled upright with the dimpled upright having a dimpled outer surface;

FIG. 3 shows an alternative embodiment of a bracket assembly mounted on a dimpled upright;

FIG. 4 shows a cross-sectional view of an alternate embodiment of a load-activated lock;

FIG. 5 shows a cross-sectional view of an alternate embodiment of a lock mounted on a dimpled upright similar to the lock shown in FIG. 2; and

FIG. 6 is an enlarged view of the bracket assembly of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention generally comprises an improved clamping system for adjustable height scaffolds that includes an upright having a dimpled upright surface comprising of peaks and valleys located thereon and a load bearing jaw of a shackle or lock having a size and shape for matingly engaging the at least one dimple of the upright to help prevent uncontrolled sliding of the adjustable height platform supports down the upright by providing for a more positive locking arrangement without damaging the dimpled upright surface.

FIG. 1 shows a perspective view of a bracket assembly 10 of the present invention mounted on a dimpled upright 11. Bracket assembly 10 includes an angle bracket 12 having a horizontal leg 13, a vertical leg 14, a load-activated lock 15, and a lower bracket cage 16. It is noted that bracket assembly 10, as shown in FIG. 1, can be used to form an adjustable height scaffold in several ways. For example bracket assembly 10 can be used in sets of four to support a platform of extended area. A short platform mounted on one bracket assembly 10 supported on upright 11 could also replace a single ladder in some applications.

Dimpled upright 11 includes an inner surface 11 a having a plurality of dimples 27 thereon and a flat or planar outer surface 11 b. Although upright 11 can be made from a variety of materials, upright 11 is preferably made of an elastically non-deformable material such as but not limited to aluminum or plastic. In regards to the dimple upright surface of the present invention, although the dimple upright surface can be secured to the upright after the upright is formed, such as an aftermarket kit, the dimple upright surface is preferable integrally formed on the upright.

In regards to angle bracket 12, vertical leg 14 of angle bracket 12 is shown in FIG. 1 as including an apertures 28 for attaching a conventional block and tackle device (not shown) or a conventional jacking device (not shown) to angle bracket 12 to enable bracket assembly 10 to be raised and lowered. Although the embodiment of FIG. 1 shows the use of angle bracket 12, alternative embodiments of the present invention can include the use of other types of brackets. For example, in an alternative embodiment, angle bracket 12 can replace with a substantially triangular-shaped bracket similar to the triangular-shaped bracket shown in U.S. Pat. No. 6,126,127 to Riblet.

The lower bracket cage 16 of bracket assembly 10, as shown in the embodiment of FIG. 1, comprises a U-shaped band 17 having a first side 17 a and a second side 17 b forming a free end 19 and a cross member 18 connecting side 17 a to side 17 b to form an attached end. Lower bracket cage 16 is coupled to angle bracket 12 through the confinement to a lower end 14 a of vertical leg 14 between sides 17 a and 17 b so that the presence of a vertical load on horizontal leg 13 of angle bracket 12 will force a roller bar 33 on bracket cage 16 against inner dimpled surface 11 a of upright 11. In further regards to lower bracket cage 16, the particular construction of the lower bracket cage is not limited to a U-shaped band and can comprise various types of bracket cages without departing from the spirit of the present invention.

In regards to load-activated lock 15, FIG. 1A shows a close-up side view of the load-activated lock 15 of FIG. 1. Load-activated lock 15, as shown in FIGS. 1 and 1A comprises a generally U-shaped band 20 having a first side member 21 and a second side member 21 a forming a free end 23 and a cross member 22 connecting side member 21 to side member 21 a. Located proximal free end 23 is an inner roller jaw 24 and located proximal cross member 22 is an outer roller jaw 25. Load-activated lock 15 also includes a mounting device for pivotally attaching load activated lock 15 to angle bracket 12 comprising a fulcrum bar 26 that extends through side members 21 and 21 a and vertical leg 14 and provides a fixed pivoting axis 26 a about which load activated lock 15 is free to pivot relative to angle bracket 12. It should be noted that fulcrum bar 26 represents any conventional device for pivotally mounting load activated lock 15 onto angle bracket 12. For example, fulcrum bar 26 can be replaced with any device, which attaches lock 15 directly to angle bracket 12 and still permits lock 15 to pivot with respect to angle bracket 12 about fulcrum pivot axis 26 a. Preferably, fulcrum bar 26 is in the form of a threaded rod that is held in place by a pair of nuts (not shown) or a pin 88 as shown in FIG. 1A.

In regards to inner roller jaw 24 and outer roller jaw 25 of load activated lock 15, inner roller jaw 24 and outer roller jaw 25 function generally as roller jaws that rollingly engage the surfaces of the upright without leaving a mark or damaging the surfaces of the upright. As such, roller jaws 24 and 25 may be used on uprights having various types of surfaces. For example, the contact surface of the upright may be a smooth aluminum surface.

A feature of the present invention is that at least one of the roller jaw engages at least one of the dimples located on a surface of the upright. Although the dimples of the dimple upright surface of the present invention can comprise of various shapes and sizes, the dimples of FIG. 1 preferably comprises a depth of less than one third the distance between the peak and valley of a dimple with each dimple shaped so that the roller jaw, pivotally mounted in the load activated lock, can engage the surface of the upright at a plurality of different transverse positions along the upright.

In the embodiment of FIG. 1, inner roller jaw 24 is sized to contact the lower side of each dimple 27 with outer jaw 25 contacting outer planar surface 11 b to securely mount bracket assembly 10 to upright 11 and support the movement of bracket assembly 10 up and down the upright 11. It is noted that a feature of the present invention is that the inner roller jaw 24 is able to roll on inner dimpled surface 11 a of upright 11 without damaging, marking or galling dimpled surface 11 a. The aforementioned feature helps reduce the upright surfaces 11 a and 11 b from being worn down through prolong and/or extensive use thereby extending the useful life of upright 11.

Since the outer roller jaw 25 comprises also a roller, load activated lock 15 further provides for a structure which will lock on upright 11 and roll up and down dimpled upright 11 without damaging upright 11.

In regards to lower bracket cage 16 and load activated lock 15, lower bracket cage 16 and load activated lock 15 cooperate to mount angle bracket 12 onto upright 13 as shown in FIG. 1. In the aforementioned manner, a pair of bracket assembly 10 can be used to create an adjustable height scaffold. Specifically, with each of the pair of bracket assembly 10 mounted onto an associated dimpled upright a scaffold is created by placing, and preferably securing, a plank across the horizontal leg 13 of each angle bracket of the pair of bracket assembly 10.

In further regards to load activated lock 15, as shown in FIGS. 1 and 1A, each of the side members 21 and 21 a of U-shaped band 20 of load activated lock 15 are shaped to include a first orifice 29 and a second orifice 30 to allow insertion of a pivot rod therethrough. First orifice 29 is disposed beneath a plane defined by fulcrum pivot axis 26 a and second orifice 30 with first and second orifices 29 and 30 shaped to allow for the insertion of a device such as a cylindrical pivot rod therethrough. That is, a pivot rod 31 extends through orifice 29 inside members 21 and 21 a to allow inner roller jaw 24 to rotate about inner roller jaw axis 24 a relative to side member 21. Similarly, outer jaw roller 25 is mounted on a pivot rod 32 that is fixedly disposed through orifice 30 in side members 21 and 21 a with pivot rod 32 sized and shaped to fit within orifice 30 to allow outer roller jaw 25 to rotate about outer jaw pivot axis 25 a relative to side member 21.

As shown in FIG. 1A, each of the ends of pivot rods 31 and 32 include a locking pin 88 attached thereto to maintain pivot rod 31 fixedly disposed through orifice 29 and pivot rod 32 fixedly disposed through orifice 30. Similar to pivot rods pivot rods 31 and 32, the ends of fulcrum bar 26 also is shown as having locking pin 88 attached thereto in order for fulcrum bar 26 to maintain the connection of side members 21 and 21 a with vertical leg 14.

It is noted that the method for rotating the inner and outer roller jaws 24 and 25 with respect to side members 21 and 21 a is not limited to the embodiment shown in FIG. 1. However, a feature of the present invention is that the inner and outer roller jaws do not damage, gall or mar the dimpled upright 11 at any region during their engagement with the surfaces of the upright, including circumstances in which the jaws happen to engage the upright surface when the bracket assembly 10 is being raised and lowered on the dimpled upright 11.

It is also noted that the load-activated lock of the present invention is not limited to a generally U-shaped band having spaced apart, parallel side members, a cross member, and free or open end. Rather, U-shaped band 20 may be replaced by alternative device, such as for example a pair of spaced apart side members. Load activated lock 15 is also not limited to the particular size and shape of side members 21 and 21 a. Rather, side members 21 and 21 a may be replaced with side members having different sizes and shapes and side members that include orifices that differ in size and shape from orifices 29 and 30.

FIG. 2 shows an alternative embodiment of a bracket assembly 34 mounted on a dimpled upright 35 having a dimpled outer surface 35 a instead of an inner dimpled surface as shown in the embodiment of FIG. 1. Unlike the bracket assembly 10 of FIG. 1, bracket assembly 34 comprises a bracket cage 36 mounted on an upper end 38 a of vertical leg 38 of an angle bracket 37, instead of on a lower end 38 b of vertical leg 38 as in bracket assembly 10. Bracket assembly 34 includes a lock 39 pivotally mounted on lower end 38 b of vertical leg 38, instead of on upper end 38 a of vertical leg 38 as in bracket assembly 10. In addition, lock 39 of bracket assembly 34 differs in construction from load activated lock 15 of bracket assembly 10 in that lock 39 includes a pair of spaced apart preferably identical side members 40 and 40 a each having a first aperture 41 that cooperate for receiving a first pivot rod (not shown) to support an inner roller jaw 44 and a second apertures 42 that cooperate for receiving a second pivot rod (not shown) to support an outer roller jaw 45. Apertures 41 and 42 are located on side members 40 and 40 a such that a fulcrum pivot axis 43 a of fulcrum bar 43 lies within the plane defined by an inner roller jaw axis 44 a and an outer roller jaw axis 45 a.

Disposing fulcrum pivot axis 43 a in the same plane as the roller jaw axes 44 a and 45 a renders lock 39 a load activated lock if a means (not shown) is provided so that outer roller jaw axis 45 a is maintained above fulcrum pivot axis 43 a, since a vertical load placed upon horizontal leg 38 of angle bracket 37 creates an inward force on inner roller jaw 44 of lock 39 or a force moving inner roller jaw 44 into engagement with upright 35 which will maintain outer roller jaw 45 in contact with dimpled outer surface 35 a of upright 35.

FIG. 3 shows an alternative embodiment of the present invention comprising a bracket assembly 46 mounted on a dimpled upright 47. Bracket assembly 46 differs from bracket assembly 10 of FIG. 1 in that bracket assembly 46 includes the use of an upper bracket cage 48 and a lower bracket cage 49 with bracket cages 48 and 49 having similar shapes. Upper and lower bracket cages 48 and 49 operate to not only capture dimpled upright 47 but also to balance the torque created by the placement of a load on a horizontal arm 51 of an angle bracket 50.

Bracket assembly 46 includes a lock 52, which differs from load-activated lock 15 of bracket assembly 10 in the location of a fulcrum bar 53 with respect to angle bracket 50. Specifically, fulcrum bar 53 of lock 52 connects the free ends of a pair of identical side members with a pair of linkage members 55 through the disposition of fulcrum bar 53 through an orifice (not shown) formed at an end of each of linkage members 55. Note that only a free end 54 a of a side member 54 is shown in FIG. 3 secured to link 55.

Linkage members 55, in turn, are coupled to angle bracket 50 by a generally cylindrical rod 56. Rod 56 provides a fixed pivoting axis about which linkage members 55 are free to rotate relative to angle bracket 50. The pivoting of the side members of lock 52 with respect to linkage members 55 enables the side members to pivot with respect to angle bracket 50. However, it should be noted that since the side members are connected indirectly to angle bracket 50, the pivot axis about which the side members pivot with respect to angle bracket 50 is not in a fixed location relative to the angle bracket 50 and is dependent on the location or position of linkage members 55.

The pivoting of linkage members 55 relative to angle bracket 50 permits both an inner roller jaw 57 and an outer roller jaw 58 of lock 52 to contact an inner surface 47 a and an outer surface 47 b of upright 47. It should be noted that the configuration of rod 53 can comprises various forms. Dimpled upright 47 of FIG. 3 also differs from the dimpled upright 11 of FIG. 1 in that the dimpled surface/outer surface 47 b of dimpled upright 47 comprises one dimple 59 instead of a plurality of dimples. The aforementioned arrangement can be convenient in situations in which the scaffold plank is located at a known fixed distance from the base of the upright such as for example in support of shelving.

FIG. 4 shows a cross-sectional view of an alternate embodiment of a load-activated lock 60 of the present invention. Load activated lock 60 includes an inner jaw 61 and outer jaw 62 which differ in construction from the inner roller jaw 24 and outer roller jaw 25 of the load activated lock 15 of FIG. 1 in that inner jaw 61 comprises an inner roller jaw 61 a and a pair of outer roller jaws 61 b.

Inner roller jaw 61 a and outer roller jaws 61 b are spaced apart on a pair of side plates so that inner roller jaw 61 a and outer roller jaws 61 b each engage a similar dimple region on a dimpled surface 64 a of dimpled upright 64. Note that only one plate 63 of pair of the side plates is shown in FIG. 4. Inner roller jaw 61 a and outer roller jaws 61 b are pivotally mounted on side plates 63 which in turn are mounted on pin 65 between a pair of preferably identical side members with only side member 66 shown in FIG. 4. Inner roller jaw 61 a and outer roller jaws 61 b are also pivotable about a pivot axis 65 a so that the roller jaws 61 a and 61 b engages the dimpled surface 64 a of upright 64 at the same time.

A feature of the embodiment of FIG. 4 is that outer roller jaws 61 b of inner jaw 61 comprises rubber cylinders mounted on pins 65 which in turn are mounted on side plates so that the rollers 61 b engages dimples 69 of dimpled inner surface 64 a when load activated lock 60 is raised or lowered without abrading, marring, or damaging dimpled surface 64 a. Inner roller jaw 61 a of inner jaw 61 comprises a metal sleeve having an inner diameter 70 greater than an outer diameter 71 of pin 65 with inner roller jaw 61 a also engaging dimples 69 of dimpled inner surface 64 a when a load activated lock 60 is raised or lowered without abrading, marring, or damaging dimpled surface 64 a. The aforementioned feature helps reduce the upright surfaces from being worn down through prolong and/or extensive use thereby extending the useful life of upright 11.

Outer jaw 62 of load activated lock 60 comprises a pair of spaced apart roller jaws 62 a and 62 b that are pivotally mounted between a pair of side plates which in turn are mounted on pin 68 between side members 66 and pivotable about a pivot axis 68 a so that roller jaws 62 a and 62 b is engageable to a flat surface 64 b of upright 64. Note that only one plate 67 of the pair of side plates is shown in FIG. 4.

In general regards to the roller jaws of the present invention, it is to be understood that the roller jaws of the present invention is not limited to a circular-shaped cross section and can comprise any cross sectional shape that allows the outer surface of the roller jaws to engage the surface of the dimpled upright continuously without abrading, marring, or damaging the surface of the dimpled upright.

FIG. 5 shows a cross-sectional view of an alternate embodiment of a lock 72 mounted on a dimpled upright 73 similar to lock 39 shown in FIG. 2. Lock 72 comprises a pair of identical side members with only one side member 75 shown. Each side member has a first orifice 76 for receiving a first crossbar 78 therethrough and a second orifice 77 for receiving a second crossbar 79 therethrough. Side member 75 also includes a third orifice 80 for receiving a fulcrum bar 85. Crossbar 78 is surrounded by a cylindrical sleeve 78 a with cylindrical sleeves 78 a dimensioned so that the inside diameter of sleeve 78 a is greater than the outer diameter of cross bar 78. Similarly, crossbar 79 is surrounded by a cylindrical sleeve 79 a with cylindrical sleeves 79 a dimensioned so that the inside diameter of sleeve 79 a is greater than the outer diameter of cross bar 79. Crossbar 78 together with cylindrical sleeves 78 a form a first roller jaw 81 and crossbar 79 together with cylindrical sleeve 79 a form a second roller jaw 82.

A dimple 74 of a dimpled surface 73 a, which comprises an inner surface of upright 73, is shown in FIG. 5 having a lower edge that is offset. Dimple 74 is also shown engaging an outer surface of cylindrical sleeve 78 a at an inner contact region 83 on dimpled surface 73 a while a flat surface 73 b comprising an outer surface of upright 73 engages an outer surface of cylindrical sleeve 79 a at an outer contact region 84 on flat surface 73 b. Inner contact region 83 and outer contact region 84 are co-linear with a fulcrum bar axis 85 a with a distance, W, between outer contact region 84 and inner contact region 83 being greater than the maximum width of dimpled upright 73 so that lock 72 can be moved up and down upright 73 by rotating lock 72 sufficiently in a counter clockwise direction. The distance between inner contact region 83 and fulcrum bar axis 85 a is shown in FIG. 5 as being denoted by a distance D and a line tangent to the dimple 74 at the inner contact region 83 is shown denoted by a tangent line TL.

In operation, the presence of a vertical force, V, applied to fulcrum bar 85 causes lock 72 to turn and bring first roller jaw 81 and second roller jaw 82 into clamping engagement with the surfaces 73 a and 73 b of upright 73. The frictional resistance from the engagement between first roller jaw 81 and dimpled surface 73 a and the frictional resistance from the engagement between second roller jaw 82 flat surface 73 b maintains lock 72 at a desired vertically stationary position on upright 73. Since the lower edge of dimple 74 is offset, when first roller jaw 81 engages dimple 74, the lower edge of dimple 74 provides a further positive resistance against uncontrolled sliding of the lock down upright 73 as lock 72 is not solely relying on the frictional resistance between the engagement of roller jaws 81, 82 with the surfaces 73 a and 73 b of upright 73.

It is noted that in the embodiment of FIG. 5, if the distance between fulcrum bar 85 and inner roller jaw 81 is sufficiently long, fulcrum bar 85 will move upward when inner roller jaw 81 is moving downward to allow lock 72 to move downward. However, as the distance between the fulcrum bar and the inner rotary jaw decreases, a region will be reached where additional friction and/or forces between the rotary jaws and the dimpled upright will be required to prevent the vertical load from falling. It is noted that the required friction will increase as the spacing between the rotary jaws and the fulcrum bar decreases.

Referring to FIG. 6, FIG. 6 shows an enlarged view of the bracket assembly 34 of FIG. 2. The dimpled upright 35 and the lock 39 of FIG. 6 are similar to the dimpled upright 73 and the lock 72 of FIG. 5. However, the embodiment of FIG. 6 differs from the embodiment of FIG. 5 in that the outer surface of dimpled upright 35 of FIG. 6 comprises a dimpled surface 35 a rather than a flat surface while the inner surface of dimpled upright 35 of FIG. 6 comprises a flat surface 35 b rather than dimpled surface 35 a.

In the operation of the embodiment of FIG. 6, when outer roller jaw 45 rotates downward on outer dimpled surface 35 a an inner contact region 86, comprising the location where inner roller jaw 44 engages upright 35, moves upwards on inner flat surface 35 b since the distance between the inner roller jaw 44 and outer roller jaw 45 is fixed. In addition, fulcrum bar 43 will also move upward to allow for the lowering of lock 39 on dimpled upright 35. The presence of a downward vertical force, V, on fulcrum bar 43 forces outer contact region 87, comprising the location where outer roller jaw 45 engages upright 35, to move upward thereby preventing the lowering of lock 39 on dimpled upright 35. In order to lower lock 39, a means must be provided to raise the fulcrum bar 43 in order to rotate lock 39 in the counter clockwise direction.

A feature of the embodiment of FIG. 6 is that unlike FIG. 5, the lock 39 of FIG. 6 is self-locking regardless of the location of the fulcrum bar 43 with respect to inner roller jaw 44. It should also be noted that the geometry of the load-activated locks of FIGS. 1, 2 and 4, is such that they are also self-locking when loaded by an angle bracket. An exception is the lock of FIG. 5 in which the lock 72 is not considered self-locking if the fulcrum bar 85 is sufficiently close to the inner roller jaw 81. 

1. A lock for prolong the life of an adjustable height scaffold comprising: a first side member and a second side member; a load bearing inner jaw and a load bearing outer jaw coupled to the side members with at least one of the jaws comprising a roller jaw having a size and shape to matingly engage with at least one dimple on a dimpled upright surface without marking or galling the dimpled upright surface while preventing uncontrolled sliding; and a mounting device adapted to couple the side members with the side members rotatable about a pivot axis of the mounting device for raising and lowering the lock.
 2. The lock of claim 1 wherein the mounting device comprises a fulcrum bar adapted to couple the side members to an angle bracket with the side members rotatable about a pivot axis of the fulcrum bar relative to the angle bracket.
 3. The lock of claim 1 wherein the first side member and the second side member form a generally U-shaped band with the side members each having an attached end and a free end.
 4. The lock of claim 3 including a pair of linkage members connecting the free end of the side members to an angle bracket with the side members rotatable about a pivot axis of the fulcrum bar relative to the linkage members.
 5. The lock of claim 2 including a bracket cage coupled to the angle bracket.
 6. The lock of claim 1 wherein the side members includes a first orifice and a second orifice with the first orifice disposed beneath a plane defined by the pivot axis of the mounting device and the second orifice.
 7. The lock of claim 1 wherein a contact region of the inner jaw and a contact region of the outer jaw are co-linear with the pivot axis of the mounting device with a distance between the contact region of the outer jaw and the contact region of the inner jaw being greater than the maximum width of an upright to enable the up and down movement of the lock on the upright through the rotation of the lock in a counter clockwise direction.
 8. The lock of claim 1 wherein the load bearing inner jaw comprises an inner roller jaw and the load bearing outer jaw comprises an outer roller jaw with the roller jaws engaging the upright surface without marking or galling the upright surface.
 9. The lock of claim 8 wherein a pivot axis of the inner roller jaw is disposed beneath a plane defined by a pivot axis of the outer roller jaw and the pivot axis of the mounting device.
 10. The lock of claim 8 wherein one of the roller jaws comprises a dimple engaging roller jaw.
 11. The lock of claim 8 wherein the lower edge of the dimple is offset to provide a positive resistance against uncontrolled sliding of the lock.
 12. The lock of claim 8 wherein the pivot axis of the mounting device is disposed in the same plane as an axis of the inner roller jaw and an axis of the outer roller jaw.
 13. The lock of claim 10 wherein the dimple engaging roller jaw includes a pair of outer roller jaws comprising rubber cylinder and an inner roller jaw located between the outer roller and comprising a metal with the roller jaws mounted between a pair of side plates.
 14. A lock for prolong the life of an adjustable height scaffold comprising: a dimpled upright surface having at least one integral dimple thereon; a pair of side members; an outer roller jaw and an inner roller jaw coupled to the side members with at least one of the roller jaws comprising a dimple engaging roller jaw having a size and shape to matingly engage with at least one dimple on the dimpled upright surface without marking or galling the dimpled upright surface to prevent uncontrolled sliding of the lock while prolong the life of the dimpled upright surface; and a fulcrum bar adapted to couple the side members to an angle bracket with the side members rotatable about an axis of the fulcrum bar relative to the angle bracket.
 15. The lock of claim 14 including an upper bracket cage and a lower bracket cage for capturing a dimpled upright and balancing the torque created by placing a load on a horizontal arm of the angle bracket.
 16. The lock of claim 14 wherein at least one of the roller jaws comprises a plurality of rollers each pivotally mounted on a pair of side plates with the plurality of rollers each having a size and shape to contact the dimpled upright surface without marking or galling the dimpled upright surface.
 17. The lock of claim 14 wherein a contact region of the inner jaw and a contact region the outer jaw are co-linear with the pivot axis of the fulcrum bar with a distance between the contact region of the outer jaw and the contact region of the inner jaw being greater than the maximum width of a dimpled upright to enable the up and down movement of the lock on the dimpled upright through rotation of the lock in a counter clockwise direction.
 18. The lock of claim 14 wherein a pivot axis of the inner roller jaw is disposed beneath a plane defined by a pivot axis of the outer roller jaw and the pivot axis of the mounting device.
 19. A lock for an adjustable height scaffold comprising: a dimpled upright surface having at least one dimple integrally form thereon; a pair of side members; an inner roller jaw and an outer roller jaw coupled to the side members with at least one of the jaws comprising a plurality of rollers each pivotally mounted on a pair of side plates with the plurality of rollers each having a size and shape to contact the dimpled upright surface without marking or galling the dimpled upright surface to prevent uncontrolled sliding of the lock on the upright while prolonging the life of the dimpled upright surface; and a fulcrum bar adapted to couple the side members to an angle bracket with the side members rotatable about an axis of the fulcrum bar relative to the angle bracket.
 20. The lock of claim 19 including a bracket cage coupled to the angle bracket. 